Need Help!- Using inductive sensors with Mach3 & C11

[George]

have obtained a quantity of nice NPN inductive sensors which I am using with the C11 board. Each sensor has a small indicator LED which lights up whenever a metallic object is within range. Lets call this the indicator.

If I connect the sensor to the +12v supply the indicator lights up whenever a metallic object is within range (approx 2mm) so far so good, they seem to work.

I'm usind two sensors wired in parallell as in the diagram attached. One will be at each end of my screws and act as linmit switches. One end will double up as the home switch.

The sensors are using an independant 12dc supply. the ground of the supply is connected to the ground of the C11 board. When I connect the output of the sensor to the input of the C11 the indicator LED lights up. It cahnges brightness when a metallic object is in range and the C11 board detects the change also. When the change is detected Mach3 does exactly as it should.
The Led on the C11 board switches on and off as it should.

OK this seems fine EXCEPT that
If I disconnect the sensors at the point marked X on the sketch then there is no difference at all in the way things are working as described above. The 12v from my external supply goes to the C11 input via a 4.7k resistor as shown. The negative of my supply for the sensors is connected to the C11 board.

This is most puzling, and lends me to believe the sensors are wrong.

Can anone help me wire these correctly ?

Many thanks

George

[zsogal]

George,

Not sure what you mean by "If I disconnect the sensors at the point marked X on the sketch then there is no difference at all in the way things are working as described above." You describe both a "so far so good" condition and also a changing of the brightness condition. And I assume that when you disconnect the switches at the point marked X the C11 board does not detect any changes. Anyway try putting a diode in series with the output of each prox switch. Also you may want to check the value of that pull-up resistor. The C11 board must have a go / no go threshold as well as the prox switches as to the max amount of current they can draw.

Zo

[George]

Hi Zo,

Thanks for your reply.


If I make a break in the wiring at the point marked x in my drawing then the sensors continue to work. i.e the C11 board detects the change and mach3 senses this. So wheteher or not the circuit is connected at that point there is no change in the way things are working. Surely this cannot be correct.

George

[Al_The_Man]

The PDF mentions 'internal 4.7k resistor' if this is a pull up from the collector then a typical 'Source Input' should work without external resistor, especially if the BOB has a pull up.
As long as a pull up exists, whether internal or external, the 4.7k in you drawing are not required.
Al.

[George]

Thanks Al,

I'm sorry to be a pain but I'm still confused. I realy dont want to blow my C11 board.

Here's a sketch from the C11 book. It shows two sensors connected in parallel but it is using two of my ports on the input to the board.
I need to save ports so can I connect the output of both the sensors to one port only ?

Or can anyone let me have a schematic of how my sensors should be wired?

Many thanks

George

[Al_The_Man]

Looking over the specs on the C11 board, it seems that the input is at 5vTTL or similar, and the fact that the sensors are not true open collector, there appears to be an internal pull up, which means when the sensor is off, the sensor operating power, 12/24vdc, could be present on the BOB input.
You could put something like either a 2N25 opto or a 2N7000 transistor to condition it for the BOB, any of these you could use in parallel to one input.
The 2N35 will give you isolation also.
If your sensors were the true open collector with no pull up, you might get away without any of the conditioning.
2N35 and 2N7000 cost a few cents.
It is too bad that many of these BOB's are not flexible to allow for up to 24vdc inputs.
Post if you need a circuit for the above.
Al.

[George]

Thanks for your patience Al,

Yes! a schematic would be very much appreciated.

Just to clarify,

I'm using two inductive sensors. Hopefully in parallel. One at each end of my main axis screw. One end will doulble up as the home switch.

Because I'm using twin screws to drive my main axis I will repeat the setup for the other screw. That's 2 of my 5 inputs to the C11 board used.

Two more inductive sensors will be used for the Y axis and two for Z axis.

Once again, many thanks.

George

Rainy Manchester UK

[Al_The_Man]

This should work, all pins on the 2N35 Opto are in parallel with the second one, with the exception of pin 2 which is the second sensor input, however only use one 270ohm resistor per pair of Opto's.
If the BOB does not have a pull up, you may need a 5k resistor from Input to 5vdc
The bottom 12vdc label should read 12dc common.
Al.

[Al_The_Man]

This should work and is a simpler version.
Use only one zener and one 5k resistor per parallel pair
Al.

[George]

Hi Al,

Many thanks, how does this look?

I take it you are taking the 5V from the C11 board ?

George

[Al_The_Man]

Although you only need one 5v zener and one 5k pull up per sensor pair.
The 5v refers to whatever supply the BOB Input uses, be it from the PC or a separate supply.
The zener just protects the input from exceeding 5v.
Al.

[George]

Thanks Al,

I think It's sunk in now, I'll try it when I get home tonight.

Cheers

George